我如何检查一个变量是否为空的Bash?
当前回答
如果变量未设置或设置为空字符串(""),则返回true。
if [ -z "$MyVar" ]
then
echo "The variable MyVar has nothing in it."
elif ! [ -z "$MyVar" ]
then
echo "The variable MyVar has something in it."
fi
其他回答
在Bash中,至少下面的命令会测试$var是否为空:
if [[ -z "$var" ]]; then
# $var is empty, do what you want
fi
指挥人测试是你的朋友。
假设Bash:
var=""
if [ -n "$var" ]; then
echo "not empty"
else
echo "empty"
fi
如果变量未设置或设置为空字符串(""),则返回true。
if [ -z "$MyVar" ]
then
echo "The variable MyVar has nothing in it."
elif ! [ -z "$MyVar" ]
then
echo "The variable MyVar has something in it."
fi
我也看到过
if [ "x$variable" = "x" ]; then ...
这显然是非常健壮和外壳无关的。
此外,“empty”和“unset”之间也有区别。请参阅如何判断字符串是否未在Bash shell脚本中定义。
检查变量v是否未设置
if [ "$v" == "" ]; then
echo "v not set"
fi